(a) Field of the Invention
The present invention relates to a variable valve lift apparatus.
(b) Description of the Related Art
Generally, a variable valve lift apparatus uses hydraulic pressure to control the opening/closing amount of a valve, or the valve operation or non-operation. More particularly, in a cylinder deactivation (CDA) system, the valve is operated or not operated by the variable valve lift apparatus, and in a variable valve lift (VVL) system, the opening/closing amount of the valve is regulated.
However, because the variable valve lift apparatus is operated by hydraulic pressure, the operating area is limited. If the engine is worn out, operating performance is deteriorated by changes in oil characteristics. In addition, the numerous hydraulic lines provide a complicated system, and necessitate additional monitoring sensors, such as a hydraulic pressure sensor and a fluid temperature sensor.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.